Enable more modular arithmetic

[sbcl.git] / doc / internals / calling-convention.texinfo

diff --git a/doc/internals/calling-convention.texinfo b/doc/internals/calling-convention.texinfo
index bf5b2f3..671ea6c 100644 (file)
--- a/doc/internals/calling-convention.texinfo
+++ b/doc/internals/calling-convention.texinfo
@@ -81,7 +81,7 @@ The local (known-values) calling convention is implemented by the
 @code{known-call-local} and @code{known-return} VOPs.
 
 Local unknown-values calls are handled at the call site by the
-@code{call-local} and @code{mutiple-call-local} VOPs. The main
+@code{call-local} and @code{multiple-call-local} VOPs. The main
 difference between the full call and local call protocols here is that
 local calls use a different frame setup protocol, and will tend to not
 use the normal frame layout for the old frame-pointer and
@@ -119,7 +119,39 @@ frame to include sufficient space for its local variables, after
 possibly converting any @code{&rest} arguments to a proper list.
 
 The above scheme was changed in 1.0.27 on x86 and x86-64 by swapping
-the old frame pointer and the return address.
+the old frame pointer with the return address and making EBP point two
+words later:
+
+On x86/x86-64 the stack now looks like this (stack grows downwards):
+
+@verbatim
+----------
+RETURN PC
+----------
+OLD FP
+---------- <- FP points here
+EMPTY SLOT
+----------
+FIRST ARG
+----------
+@end verbatim
+
+just as if the function had been CALLed and upon entry executed the
+standard prologue: PUSH EBP; MOV EBP, ESP. On other architectures the
+stack looks like this (stack grows upwards):
+
+@verbatim
+----------
+FIRST ARG
+----------
+EMPTY SLOT
+----------
+RETURN PC
+----------
+OLD FP
+---------- <- FP points here
+@end verbatim
+
 
 @node Unknown-Values Returns
 @comment  node-name,  next,  previous,  up
@@ -159,7 +191,7 @@ EBX} instruction. When expecting more than one value, we need to
 arrange to set up default values when a single-value return happens,
 so we encode a jump around a stub of code which fakes up the register
 use convention of a multiple-value return. Again, in the old
-convention this was a two-byte unconditionl jump, and in the new
+convention this was a two-byte unconditional jump, and in the new
 convention this is a conditional jump based on the carry flag.
 
 
@@ -180,9 +212,11 @@ the case of an entry point for a full call).
 @comment  node-name,  next,  previous,  up
 @section Additional Notes
 
-The low-hanging fruit here is going to be changing every call and
-return to use @code{CALL} and @code{RETURN} instructions instead of
-@code{JMP} instructions.
+The low-hanging fruit is going to be changing every call and return to
+use @code{CALL} and @code{RETURN} instructions instead of @code{JMP}
+instructions which is partly done on x86oids: a trampoline is
+@code{CALL}ed and that @code{JMP}s to the target which is sufficient
+to negate (most of?) the penalty.
 
 A more involved change would be to reduce the number of argument
 passing registers from three to two, which may be beneficial in terms